1. Field of the Invention
The present invention relates to a press working method for continuously manufacturing products having various different lengths depending upon demand and a small thickness. More particularly, it relates to a method of manufacturing thin but lengthy metallic products by press working from a plate-like material fed from a source of material such as a roll of substantially thin metallic strip. The present invention is preferably but non-exclusively applicable to press working processes for manufacturing header plates used as parts of a refrigerant condenser accommodated in an air-conditioning apparatus.
2. Description of the Related Art
It is well known that when a thin but lengthy metallic product is manufactured from a plate-like metallic workpiece by a press working including bending, coining, and perforating processes, the workpiece is apt to be undesirably stretched in a longitudinal direction thereof, i.e., in the direction corresponding to a direction in which the metallic raw workpiece is fed during the bending and coining processes. Further, the amount of stretch of the workpiece in the longitudinal direction thereof varies depending on a change in the width and thickness of the plate-like workpiece, and accordingly, positions of the workpiece to which the coining working is applied are often out of registration with positions to which the perforating working is applied. Moreover, spacings between two neighboring perforations cannot be constant. Consequently, high-quality press work products cannot be obtained.
In order to obviate the above-mentioned defects encountered by the conventional press working method, several proposals have been provided. For example, Japanese Unexamined Patent publications (Kokai) Nos. 3-264139 and 4-43298 disclose an improved method of manufacturing assembling parts of an heat exchanger for a car air-conditioning apparatus by using a press working method.
FIG. 16 schematically illustrates the above-mentioned improved press working method adopted for manufacturing the assembling parts of the heat exchanger according to the disclosure of the two Japanese publications.
Referring to FIG. 16, a flat, plate-like workpiece 101 having predetermined width and length is prepared at a preparatory stage (A) by severing a metallic raw material. Subsequently, the workpiece 101 is fed in a direction shown by an arrow, which is perpendicular to the longitudinal direction of the workpiece 101, into a press machine provided with transfer-type dies or robotic dies.
In the press machine, the workpiece 101 is initially subjected to a bending process (B) in which the workpiece 101 is formed with bent portions 102 on both sides thereof. The workpiece 101 is further subjected to a coining process (C) and to a perforating process (D) at substantially the same time. In the coining and perforating processes (C) and (D), a plurality of concavities 103 are formed in an intermediate portion of the workpiece 101 between the bent portions 102 by applying a compression to the intermediate portion, and a plurality of perforations 104 are punched in respective concavities 103 of the workpiece 101.
Nevertheless, in the above-mentioned known press working method, when products having many different lengths (for example, header plates having 40 different lengths are conventionally used for assembling various refrigerant condensers of air-conditioning apparatuses.) are manufactured, respective pressing dies for respective products of different lengths are required, and accordingly, a production cost for respective pressing dies must greatly increase.
Moreover, when a press working of the products is daily carried out, a preparatory process for changing pressing dies must be repeated many times according to demand resulting in interruption of the press working process. Namely, a lot of time must be consumed by changing the pressing dies every day. As a result, the rate of operation of the respective pressing dies is low.